<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Title</title>
    </head>
    <body>
        <img src="img/menu.png" alt="" id="btn">
    </body>
    <script>
        var btn=document.getElementById("btn");
        btn.onclick=function () {
            alert(35)
        }
    </script>
</html>